1. Field of the Invention
This invention relates to a rotary head type digital signal recording and reproducing apparatus and to a digital signal recording and reproducing method for digitally recording the video and audio signals on a magnetic tape.
2. Description of the Related Art
Conventionally, various systems of rotary head type digital signal recording and reproducing apparatus have been developed. As a typical example of such apparatuses, a digital VTR for a broadcasting service known as a D-2 system will be given an explanation hereinafter.
FIG. 1 is a schematic block diagram showing one example of the D-2 system for a digital VTR. In the figure, numeral 101 is an input terminal for a video signal, via which an analog video signal enters an A/D converter 103, which converts the analog video signal to a digital signal and outputs the digital video signal to a digital recording signal processor 105. On the other hand, numeral 102 is an input terminal for an audio signal, via which an analog audio signal enters an A/D converter 104, which converts the analog audio signal to a digital signal and outputs the digital audio signal to the digital recording signal processor 105. The digital recording signal processor 105 carries out error-correction encoding, digital modulation, etc. and outputs the processed signal to recording AMPs 106, 107. The recording AMPs 106, 107 amplify input signals. The amplified signal is distributed to four recording and reproducing heads 112, 113, 114 and 115 via recording/reproducing selecting switches 108 and 109 and via head selection switches 110, 111 and is recorded on a magnetic tape (not shown). Numerals 116-122 show components of a reproducing part, where reproducing AMPs 116 and 117 amplify signals which are reproduced on recording and reproducing heads 112, 113, 114, 115 and are transferred through switches 110, 111 and through switches 108, 109, and then the amplified signals are output to a digital reproducing signal processor 118. The digital reproducing signal processor 118 carries out digital demodulation and error-correction decoding etc., and outputs video and audio signals of normal signal strings to D/A converters 119 and 120. The D/A converter 119 converts the input signal to the original analog video signal and outputs the analog video signal via an output terminal 121. The D/A converter 120 converts the input signal to the original analog audio signal and outputs the analog audio signal via an output terminal 122.
FIG. 2 shows a tape format of the D-2 system for a digital VTR. As shown in FIG. 2, in the D-2 system, a cue, time record, and control tracks are provided in the longitudinal direction of the magnetic tape. On the track tilted in the longitudinal direction of the magnetic tape, video and audio signals are digitally recorded. The audio signal is arranged in a total of four channels; the video signals are sandwiched by four channels with two channels on either side.
Referring now to FIG. 1, operations will be described in detail hereinafter. A composite video signal supplied to the input terminal 101 is sampled at a quadruple subcarrier frequency (14.318 MHz) and is converted into the digital signal of 8 quantized bits (at the A/D converter 103). The audio signal supplied to the input terminal 102 is sampled at 48 kHz and is converted into the digital signal of 20 quantized bits (at the A/D converter 104). In FIG. 1, for simplification, the audio signal input is represented by one channel but, in practice, a four channel audio signal is supplied. The digitized video and four-channel audio signals are supplied to the digital recording signal processor 105. At the digital recording signal processor 105, the video and four-channel audio signals are time-base-processed and at the same time error-correcting codes are assigned to these signals in accordance with the format. The error-correcting codes are separately assigned to the respective video and four-channel audio signals. The digital recording signal processor 105 further performs digital modulation processing in accordance with a specified modulation system. The output signal of digital recording signal processor 105 is distributed to the recording and reproducing heads 112, 113, 114, and 115, respectively, by the head selection switches 110 and 111 via recording AMPs 106, 107 as well as recording/reproducing selecting switches 108, 109, and is recorded on a magnetic tape in accordance with the tape format shown in FIG. 2. In this system, the data rate after the error-correcting code assigning is 127 Mbit/sec, and in terms of the video signal, the data for 1 field is divided to be recorded in 6 tracks.
The recorded signal is reproduced as follows. The signal reproduced by the recording and reproducing heads 112, 113, 114, 115 enters the digital reproducing signal processor 118 after being passed through head selection switches 110 and 111 as well as the recording/reproducing selecting switches 108 and 109 and amplified by the reproducing AMPs 116, 117. The digital reproducing signal processor 118 performs digital demodulation and error-correction decoding and the signal is decoded into the normal video signal data string and the 4-channel audio signal data string to be outputted. The output signal of the digital reproducing signal processor 118 is returned to the original video and 4-channel audio signals by the D/A converters 119, 120 and outputted via the output terminals 121, 122.
FIG. 3 shows a schematic block diagram for another conventional configuration of the D-2 system for a digital VTR. Numeral 201 in the figure is an A/D converter which converts analog video and 4-channel audio signals into digital signals, respectively. A video signal processor 202, a first audio signal processor 203a, a second audio signal processor 203b, a third audio signal processor 203c, and a fourth audio signal processor 203d sample an output digital signal from each A/D converter 201 at a specified frequency and output the sampled output digital signal to a corresponding first digital signal processor 204a and second digital signal processors 204b, 204b, 204b, 204b. Each of the first and second digital signal processors 204a, 204b assigns error-correcting codes to the signal and then outputs the signal to a digital signal processor 206 via a switch 205. The digital signal processor 206 performs digital modulation processing on the input signal and then outputs the signal to a recording AMP 207. The recording AMP 207 amplifies the input signal. The amplified signal is recorded on a magnetic tape (not shown) by a recording and reproducing head 209 via a recording/reproducing selector switch 208. Numeral 210 is a reproduction unit which is so configured that the process is carried out in reverse sequence to that in the recording unit and therefore, the internal configuration of which is omitted.
Because the D-2 system is standardized as a digital VTR for broadcasting, azimuth recording is performed without a guard band between tracks in the D-2 format. As shown in FIG. 2, the audio signal, the video signal, and the audio signal are arranged in this order in the head scanning direction and the audio signal is arranged in two channels each on either edge of the track, and form a total of four channels. In the D-2 composite system, one line of the video signal is made to contain 910 samples by sampling at 4 f.sub.sc, four times the subcarrier. After the 768 samples excluding the horizontal synchronizing signal are divided into two channels with the vertical synchronizing signal being excluded, the samples in 1/3 of the field of 85 lines are collected and the order of 384.times.85.times.8 bits of data are rearranged by shuffling. An error-correcting code is assigned to the data and the data are recorded as a track pattern. FIG. 4 shows a format in which a video signal area and an audio signal area are error-correcting-encoded. The pixel data of one field are divided into three portions, separated into even numbered samples and odd numbered samples and recorded in separate tracks. One field consists of six tracks and the pattern format of each track is identical.
Now referring to FIG. 3, operations are briefly explained. The audio signal supplied to the input terminal is converted into a 20-bit digital signal by the A/D converter 201. Sampling is performed at 48 kHz. The error-correcting codes are assigned separately to the video signal and the audio signal at the digital signal processors 204a, 204b, respectively. Further, at the digital signal processor 206, digital modulation processing is performed in accordance with a specified modulation format. The output of the digital signal processor 206 is passed through the recording AMP 207 as well as the recording/reproducing selector switch 208, distributed to the recording and reproducing head 209 by the head selection switch (not shown), and recorded on a magnetic tape in accordance with a tape format. In this system, the data rate, after an error-correction code is assigned, is 127 Mbit/sec and in terms of the video signals, the data of one field are divided into 6 tracks to be recorded.
As described above, because in this format, the audio signal is separately recorded in four individual channels, editing can be performed independently for each channel. In order to perform editing independently for each channel, a track format in which the audio signal of one channel is recorded as one area is required. In short, an area dividing type track format is required. Then, a gap between the areas is also required. In addition, because the data rate of the video and audio signals are different, the video signal area is large, while the audio signal is smaller than the video signal area. Consequently, in order to give the audio signal area error correction capability equivalent to that of the video signal area, for example, in the D-2 format audio code (12, 8, 5) Reed-Solomon codes may be so arranged that the codes keep an equal distance with each other as in the video C2 code (68, 64, 5) Reed-Solomon codes wherein, (n, k, d) represent the code length by n, information length by k, and the distance between codes by d. However, the equivalent error-correcting capability may be obtained but the encoding efficiency becomes extremely poor; 8/12 for the audio signal against 64/68 for the video signal.
Because the digital VTR for broadcasting apparatuses is configured as described above, the digital VTR has appropriate qualities for business use such as high reliability, high picture quality, high sound quality, and highly sophisticated editing. Yet, on the other hand, because the digital VTR employs an area dividing type format as described above, gaps must be provided and in addition, when the equal error correcting capabilities are given to both the video and audio signals, the encoding efficiency of the audio signal decreases. In home digital VTR, compactness and user-friendliness are strongly required as is the case with presently available VTRs equipped with a camera in the market.